Satunnaistus

Satunnaistus is the process of introducing randomness into the assignment of units, treatments, or outcomes, rather than deciding them deterministically. It is used to reduce bias, balance known and unknown confounding factors, and enable valid statistical inference.

In experimental design, random assignment of participants to treatment and control groups is standard practice. Common schemes include simple randomization, block randomization to ensure balance within subgroups, and stratified randomization to preserve key characteristics. Randomization is typically achieved with random number generators, shuffled lists, or other unpredictable methods, and allocation concealment helps prevent selection bias by keeping future assignments hidden from researchers and participants.

Applications span clinical trials, social science experiments, and software development through A/B testing. In addition, randomization underpins Monte Carlo simulations and other computational methods that model variability by repeatedly sampling from probability distributions. The approach is also used in survey sampling to select representative subsets of a population.

Risks and limitations involve incomplete blinding, noncompliance, dropouts, or differential follow-up, which can introduce bias if the randomization procedure is not properly implemented or analyzed. Predefined randomization schemes and intention-to-treat analyses help mitigate these issues and preserve the validity of conclusions.

Historically, the emphasis on randomization grew with the development of modern experimental design in the early 20th century, notably in the work of statisticians such as Ronald Fisher. In Finnish usage, satunnaistus or satunnaistaminen denotes the process of introducing randomness in a controlled way.

See also: satunnaistaminen, random sampling, random number generation, Monte Carlo methods, A/B testing.